Surgical Access System and Related Methods

ABSTRACT

A surgical access system including a tissue distraction assembly and a tissue retraction assembly, both of which may be equipped with one or more electrodes for use in detecting the existence of (and optionally the distance and/or direction to) neural structures before, during, and after the establishment of an operative corridor to a surgical target site. Some embodiments of the surgical access system may be particularly suited for establishing an operative corridor to a surgical target site in the spine. Such an operative corridor may be established through the retroperitoneal space and the psoas muscle during a direct lateral, retroperitoneal approach to the spine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/071,540 (filed on Mar. 16, 2016), now pending, which is acontinuation of U.S. patent application Ser. No. 14/066,098 (filed onOct. 29, 2013), now U.S. Pat. No. 9,314,152, entitled “Surgical AccessSystem and Related Methods,” which is a continuation of U.S. patentapplication Ser. No. 12/983,627 (filed on Jan. 3, 2011), now U.S. Pat.No. 8,591,432, entitled “Surgical Access System and Related Methods,”which is a continuation of U.S. patent application Ser. No. 12/635,869(filed on Dec. 11, 2009), now U.S. Pat. No. 8,303,515, entitled“Surgical Access System and Related Methods,” which is a continuation ofU.S. patent application Ser. No. 10/967,668 (filed on Oct. 18, 2004),now U.S. Pat. No. 7,905,840, entitled “Surgical Access System andRelated Methods,” which claims the benefit of priority from U.S.Provisional Patent Application Ser. No. 60/512,594 (filed on Oct. 17,2003) entitled “System and Methods for Performing Lateral LumbarSurgery,” the entire contents of all these rpior applications are herebyexpressly incorporated by reference into this disclosure as if set forthfully herein. The present application also incorporates by reference thefollowing co-assigned patent applications in their entireties: PCT App.Ser. No. PCT/US02/22247, entitled “System and Methods for DeterminingNerve Proximity, Direction, and Pathology During Surgery,” filed on Jul.11, 2002; PCT App. Ser. No. PCT/US02/30617, entitled “System and Methodsfor Performing Surgical Procedures and Assessments,” filed on Sept. 25,2002; PCT App. Ser. No. PCT/US02/35047, entitled “System and Methods forPerforming Percutaneous Pedicle Integrity Assessments,” filed on Oct.30, 2002; and PCT App. Ser. No. PCT/US03/02056, entitled “System andMethods for Determining Nerve Direction to a Surgical Instrument,” filedJan. 15, 2003 (collectively “NeuroVision PCT Applications”).

BACKGROUND OF THE INVENTION I. Field of the Invention

The present invention relates generally to systems and methods forperforming surgical procedures and, more particularly, for accessing asurgical target site in order to perform surgical procedures.

II. Discussion of the Prior Art

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. The access systems developed to date,however, fail in various respects to meet all the needs of the surgeonpopulation.

One drawback associated with prior art surgical access systems relatesto the ease with which the operative corridor can be created, as well asmaintained over time, depending upon the particular surgical targetsite. For example, when accessing surgical target sites located beneathor behind musculature or other relatively strong tissue (such as, by wayof example only, the psoas muscle adjacent to the spine), it has beenfound that advancing an operative corridor-establishing instrumentdirectly through such tissues can be challenging and/or lead to unwantedor undesirable effects (such as stressing or tearing the tissues). Whilecertain efforts have been undertaken to reduce the trauma to tissuewhile creating an operative corridor, such as (by way of example only)the sequential dilation system of U.S. Pat. No. 5,792,044 to Foley etal., these attempts are nonetheless limited in their applicability basedon the relatively narrow operative corridor. More specifically, based onthe generally cylindrical nature of the so-called “working cannula,” thedegree to which instruments can be manipulated and/or angled within thecannula can be generally limited or restrictive, particularly if thesurgical target site is a relatively deep within the patient.

Efforts have been undertaken to overcome this drawback, such as shown inU.S. Pat. No. 6,524,320 to DiPoto, wherein an expandable portion isprovided at the distal end of a cannula for creating a region ofincreased cross-sectional area adjacent to the surgical target site.While this system may provide for improved instrument manipulationrelative to sequential dilation access systems (at least at deep siteswithin the patient), it is nonetheless flawed in that the deployment ofthe expandable portion may inadvertently compress or impinge uponsensitive tissues adjacent to the surgical target site. For example, inanatomical regions having neural and/or vasculature structures, such ablind expansion may cause the expandable portion to impinge upon thesesensitive tissues and cause neural and/or vasculature compromise, damageand/or pain for the patient.

This highlights yet another drawback with the prior art surgical accesssystems, namely, the challenges in establishing an operative corridorthrough or near tissue having major neural structures which, ifcontacted or impinged, may result in neural impairment for the patient.Due to the threat of contacting such neural structures, efforts thus farhave largely restricted to establishing operative corridors throughtissue having little or substantially reduced neural structures, whicheffectively limits the number of ways a given surgical target site canbe accessed.

This can be seen, by way of example only, in the spinal arts, where theexiting nerve roots and neural plexus structures in the psoas musclehave rendered a lateral or far lateral access path (so-calledtrans-psoas approach) to the lumbar spine virtually impossible. Instead,spine surgeons are largely restricted to accessing the spine from theposterior (to perform, among other procedures, posterior lumbarinterbody fusion (PLIF)) or from the anterior (to perform, among otherprocedures, anterior lumbar interbody fusion (ALIF)).

Posterior-access procedures involve traversing a shorter distance withinthe patient to establish the operative corridor, albeit at the price ofoftentimes having to reduce or cut away part of the posterior bonystructures (i.e. lamina, facets, spinous process) in order to reach thetarget site (which typically comprises the disc space). Anterior-accessprocedures are relatively simple for surgeons in that they do notinvolve reducing or cutting away bony structures to reach the surgicaltarget site. However, they are nonetheless disadvantageous in that theyrequire traversing through a much greater distance within the patient toestablish the operative corridor, oftentimes requiring an additionalsurgeon to assist with moving the various internal organs out of the wayto create the operative corridor.

The present invention is directed at eliminating, or at least minimizingthe effects of, the above-identified drawbacks in the prior art.

SUMMARY OF THE INVENTION

The present invention accomplishes this goal by providing a novel accesssystem and related methods which involve detecting the existence of (andoptionally the distance and/or direction to) neural structures before,during, and after the establishment of an operative corridor through (ornear) any of a variety of tissues having such neural structures which,if contacted or impinged, may otherwise result in neural impairment forthe patient. It is expressly noted that, although described hereinlargely in terms of use in spinal surgery, the access system of thepresent invention is suitable for use in any number of additionalsurgical procedures wherein tissue having significant neural structuresmust be passed through (or near) in order to establish an operativecorridor.

According to one broad aspect of the present invention, the accesssystem comprises a tissue distraction assembly and a tissue retractionassembly, both of which may be equipped with one or more electrodes foruse in detecting the existence of (and optionally the distance and/ordirection to) neural structures. The tissue distraction assembly (inconjunction with one or more elements of the tissue retraction assembly)is capable of, as an initial step, distracting a region of tissuebetween the skin of the patient and the surgical target site. The tissueretraction assembly is capable of, as a secondary step, being introducedinto this distracted region to thereby define and establish theoperative corridor. Once established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated within the operative corridor depending upon the givensurgical procedure. The electrode(s) are capable of, during both tissuedistraction and retraction, detecting the existence of (and optionallythe distance and/or direction to) neural structures such that theoperative corridor may be established through (or near) any of a varietyof tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly may include any number of componentscapable of performing the necessary distraction. By way of example only,the tissue distraction assembly may include a K-wire, an initial dilatorof split construction, and one or more dilators of traditional (that is,non-split) construction for performing the necessary tissue distractionto receive the remainder of the tissue retractor assembly thereafter.One or more electrodes may be provided on one or more of the K-wire anddilator(s) to detect the presence of (and optionally the distance and/ordirection to) neural structures during tissue distraction.

The tissue retraction assembly may include any number of componentscapable of performing the necessary retraction. By way of example only,the tissue retraction assembly may include one or more retractor bladesextending from a handle assembly. The handle assembly may be manipulatedto open the retractor assembly; that is, allowing the retractor bladesto separate from one another (simultaneously or sequentially) to createan operative corridor to the surgical target site. In a preferredembodiment, this is accomplished by maintaining a posterior retractorblade in a fixed position relative to the surgical target site (so as toavoid having it impinge upon any exiting nerve roots near the posteriorelements of the spine) while the additional retractor blades (i.e.cephalad-most and caudal-most blades) are moved or otherwise translatedaway from the posterior retractor blade (and each other) so as to createthe operative corridor in a fashion that doesn't infringe upon theregion of the exiting nerve roots.

The retractor blades may be optionally dimensioned to receive and directa rigid shim element to augment the structural stability of theretractor blades and thereby ensure the operative corridor, onceestablished, will not decrease or become more restricted, such as mayresult if distal ends of the retractor blades were permitted to “slide”or otherwise move in response to the force exerted by the displacedtissue. In a preferred embodiment, only the posterior retractor blade isequipped with such a rigid shim element. In an optional aspect, thisshim element may be advanced into the disc space after the posteriorretractor blade is positioned, but before the retractor is opened intothe fully retracted position. The rigid shim element is preferablyoriented within the disc space such that is distracts the adjacentvertebral bodies, which serves to restore disc height. It alsopreferably advances a sufficient distance within the disc space(preferably past the midline), which serves the dual purpose ofpreventing post-operative scoliosis and forming a protective barrier(preventing the migration of tissue (such as nerve roots) into theoperative field and the inadvertent advancement of instruments outsidethe operative field).

The retractor blades may optionally be equipped with a mechanism fortransporting or emitting light at or near the surgical target site toaid the surgeon's ability to visualize the surgical target site,instruments and/or implants during the given surgical procedure.According to one embodiment, this mechanism may comprise, but need notbe limited to, coupling one or more light sources to the retractorblades such that the terminal ends are capable of emitting light at ornear the surgical target site. According to another embodiment, thismechanism may comprise, but need not be limited to, constructing theretractor blades of suitable material (such as clear polycarbonate) andconfiguration such that light may be transmitted generally distallythrough the walls of the retractor blade light to shine light at or nearthe surgical target site. This may be performed by providing theretractor blades having light-transmission characteristics (such as withclear polycarbonate construction) and transmitting the light almostentirely within the walls of the retractor blade (such as by frosting orotherwise rendering opaque portions of the exterior and/or interior)until it exits a portion along the interior (or medially-facing) surfaceof the retractor blade to shine at or near the surgical target site. Theexit portion may be optimally configured such that the light is directedtowards the approximate center of the surgical target site and may beprovided along the entire inner periphery of the retractor blade or oneor more portions therealong.

According to another aspect of the invention, a minimally invasivelateral lumber surgery may be performed using various embodiments of thesurgical access system. The surgical method may be accomplished byguiding at least a portion of the tissue distraction assembly to thesurgical target site using a lateral, retroperitoneal approach.According to some embodiments, the access system is used to access thelumbar spine via a direct lateral, retroperitoneal approach. In suchembodiments, blunt finger dissection may be used to safely enter theretroperitoneal space posteriorly and sweep the peritoneal cavityanteriorly. A distal end of the K-wire, and possibly other components ofthe tissue distraction assembly, are then escorted through theretroperitoneal space to the psoas muscle utilizing finger dissection.In some instances, the initial dilator is guided through theretroperitoneal space by a finger in contact with the distal end, so thepotential of peritoneal disruption may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of a tissue retraction assembly (in use)forming part of a surgical access system according to the presentinvention;

FIGS. 2-3 are perspective views illustrating the front and back of ashim element for use with a posterior retractor blade of the retractoraccording to the retractor of the present invention;

FIGS. 4-5 are perspective views illustrating the front and back of anarrow retractor extender for use with one of a cephalad and caudalretractor blade according to the retractor of the present invention;

FIGS. 6-7 are perspective views illustrating the front and back of awide retractor extender for use with one of a cephalad and caudalretractor blade according to the retractor of the present invention;

FIG. 8 is a perspective, partially exploded view of the retractorassembly of the present invention, without the retractor blades;

FIG. 9 is a perspective view illustrating the components and use of aninitial distraction assembly (i.e. K-wire, an initial dilating cannulawith handle, and a split-dilator housed within the initial dilatingcannula) forming part of the surgical access system according to thepresent invention, for use in distracting to a surgical target site(i.e. annulus);

FIG. 10 is a perspective view illustrating the K-wire and split-dilatorof the initial distraction assembly with the initial dilating cannulaand handle removed;

FIG. 11 is a posterior view of the vertebral target site illustratingthe split-dilator of the present invention in use distracting in agenerally cephalad-caudal fashion according to one aspect of the presentinvention;

FIG. 12 is a side view illustrating the use of a secondary distractionassembly (comprising a plurality of dilating cannulae over the K-wire)to further distract tissue between the skin of the patient and thesurgical target site according to the present invention;

FIG. 13 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending there from (posterior, cephalad-most, and caudal-most)disposed over the secondary distraction assembly of FIG. 12 (shown in afirst, closed position);

FIG. 14 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending there from (posterior, cephalad-most, and caudal-most)with the secondary distraction assembly of FIG. 12 removed and shimelement introduced;

FIGS. 15-16 are perspective and top views, respectively, of theretractor assembly in a second, opened (i.e. retracted) position tothereby create an operative corridor to a surgical target site accordingto the present invention;

FIGS. 17-18 are perspective and side views, respectively, of theretractor assembly in the second, opened (i.e. retracted) position (withthe secondary distraction assembly removed) and with the retractorextenders of FIGS. 4-5 and 6-7 coupled to the retractor according to thepresent invention.

FIG. 19 is a perspective view of an exemplary nerve monitoring systemcapable of performing nerve monitoring before, during and after thecreating of an operative corridor to a surgical target site using thesurgical access system in accordance with the present invention;

FIG. 20 is a block diagram of the nerve monitoring system shown in FIG.19; and

FIGS. 21-22 are screen displays illustrating exemplary features andinformation communicated to a user during the use of the nervemonitoring system of FIG. 19.

FIGS. 23-50 illustrate a method for accessing a surgical target site inthe spine using a substantially lateral, retroperitoneal approach.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. The surgical accesssystem disclosed herein boasts a variety of inventive features andcomponents that warrant patent protection, both individually and incombination.

The present invention involves accessing a surgical target site in afashion less invasive than traditional “open” surgeries and doing so ina manner that provides access in spite of the neural structures requiredto be passed through (or near) in order to establish an operativecorridor to the surgical target site. Generally speaking, the surgicalaccess system of the present invention accomplishes this by providing atissue distraction assembly and a tissue retraction assembly, both ofwhich may be equipped with one or more electrodes for use in detectingthe existence of (and optionally the distance and/or direction to)neural structures. In some embodiments, the surgical access system maybe used access a surgical target site on the spine via a substantiallylateral, retroperitoneal approach (as shown, for example, in FIGS.23-50).

These electrodes are preferably provided for use with a nervesurveillance system such as, by way of example, the type shown anddescribed in the co-pending and commonly assigned NeuroVision PCTApplications referenced above, the entire contents of which areexpressly incorporated by reference as if set forth herein in theirentirety. Generally speaking, this nerve surveillance system is capableof detecting the existence of (and optionally the distance and/ordirection to) neural structures during the distraction and retraction oftissue by detecting the presence of nerves by applying a stimulationsignal to such instruments and monitoring the evoked EMG signals fromthe myotomes associated with the nerves being passed by the distractionand retraction systems of the present invention. In so doing, the systemas a whole (including the surgical access system of the presentinvention) may be used to form an operative corridor through (or near)any of a variety of tissues having such neural structures, particularlythose which, if contacted or impinged, may otherwise result in neuralimpairment for the patient. In this fashion, the access system of thepresent invention may be used to traverse tissue that would ordinarilybe deemed unsafe or undesirable, thereby broadening the number ofmanners in which a given surgical target site may be accessed.

The tissue distraction assembly of the present invention (comprising aK-wire, an initial dilator, and a split-dilator disposed within theinitial dilator) is employed to distract the tissues extending betweenthe skin of the patient and a given surgical target site (preferablyalong the posterior region of the target intervertebral disc). Asecondary distraction assembly (i.e. a plurality of sequentiallydilating cannulae) may optionally be employed after the initialdistraction assembly to further distract the tissue. Once distracted,the resulting void or distracted region within the patient is ofsufficient size to accommodate a tissue retraction assembly of thepresent invention. More specifically, the tissue retraction assembly(comprising a plurality of retractor blades extending from a handleassembly) may be advanced relative to the secondary distraction assemblysuch that the retractor blades, in a first, closed position, areadvanced over the exterior of the secondary distraction assembly. Atthat point, the handle assembly may be operated to move the retractorblades into a second, open or “retracted” position to create anoperative corridor to the surgical target site.

According to one aspect of the invention, following (or before) thisretraction, a posterior shim element (which is preferably slideablyengaged with the posterior retractor blade) may be advanced such that adistal shim extension in positioned within the posterior region of thedisc space. If done before retraction, this helps ensure that theposterior retractor blade will not move posteriorly during theretraction process, even though the other retractor blades (i.e.cephalad-most and caudal-most) are able to move and thereby create anoperative corridor. Fixing the posterior retractor blade in this fashionserves several important functions. First, the distal end of the shimelement serves to distract the adjacent vertebral bodies, therebyrestoring disc height. It also rigidly couples the posterior retractorblade in fixed relation relative to the vertebral bodies. The posteriorshim element also helps ensure that surgical instruments employed withinthe operative corridor are incapable of being advanced outside theoperative corridor, preventing inadvertent contact with the exitingnerve roots during the surgery. Once in the appropriate retracted state,the cephalad-most and caudal-most retractor blades may be locked inposition and, thereafter, retractor extenders advanced therealong toprevent the ingress or egress of instruments or biological structures(i.e. nerves, vasculature, etc.) into or out of the operative corridor.Once the operative corridor is established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated within the operative corridor depending upon the givensurgical procedure.

FIG. 1 illustrates a tissue retraction assembly 10 forming part of asurgical access system according to the present invention. Theretraction assembly 10 includes a plurality of retractor bladesextending from a handle assembly 20. By way of example only, the handleassembly 20 is provided with a first retractor blade 12, a secondretractor blade 16, and a third retractor blade 18. The retractorassembly 10 is shown in a fully retracted or “open” configuration, withthe retractor blades 12, 16, 18 positioned a distance from one anotherso as to form an operative corridor 15 there between and extending to asurgical target site (e.g. an annulus of an intervertebral disc).Although shown and described below with regard to the three-bladedconfiguration, it is to be readily appreciated that the number ofretractor blades may be increased or decreased without departing fromthe scope of the present invention. Moreover, although described andshown herein, for example in FIGS. 1, 9-18, and 23-50, with reference toa generally lateral approach to a spinal surgical target site (with thefirst blade 12 being the “posterior” blade, the second blade 16 beingthe “cephalad-most” blade, and the third blade 18 being the“caudal-most” blade), it will be appreciated that the retractor assembly10 of the present invention may find use in any number of differentsurgical approaches, including generally posterior, generallypostero-lateral, generally anterior and generally antero-lateral.

The retractor blades 12, 16, 18 may be equipped with various additionalfeatures or components. By way of example only, posterior retractorblade 12 may be equipped with a shim element 22 (shown more clearly inFIGS. 2-3). Shim element 22 serves to distract the adjacent vertebralbodies (thereby restoring disc height), helps secure the retractorassembly 10 relative to the surgical target site, and forms a protectivebarrier to prevent the ingress or egress of instruments or biologicalstructures (i.e. nerves, vasculature, etc.) into or out of the operativecorridor. Each of the remaining retractor blades (cephalad-most blade 16and caudal-most blade 18) may be equipped with a retractor extender,such as the narrow retractor extender 24 shown in FIGS. 4-5 or the wideretractor extender 25 shown in FIGS. 6-7. The retractor extenders 24/25extend from the cephalad-most and caudal-most retractor blades 16, 18 toform a protective barrier to prevent the ingress or egress ofinstruments or biological structures (i.e. nerves, vasculature, etc.)into or out of the operative corridor 15.

According to the present invention, any or all of the retractor blades12, 16, 18, the shim element 22 and/or the retractor extenders 24/25 maybe provided with one or more electrodes 39 (preferably at their distalregions) equipped for use with a nerve surveillance system, such as, byway of example, the type shown and described in the NeuroVision PCTApplications. Each of the shim element 22 and/or the retractor extenders24/25 may also be equipped with a mechanism to selectively andreleasably engage with the respective retractor blades 12, 16, 18. Byway of example only, this may be accomplished by configuring the shimelement 22 and/or the retractor extenders 24/25 with a tab element 27capable of engaging with corresponding rachet-like grooves (shown at 29in FIG. 1) along the inner-facing surfaces of the retractor blades 12,16, 18. Each of the shim element 22 and/or the retractor extenders 24/25is provided with a pair of engagement elements 37 having, by way ofexample only, a generally dove-tailed cross-sectional shape. Theengagement elements 37 are dimensioned to engage with receiving portionson the respective retractor blades 12, 16, 18. In a preferredembodiment, each of the shim element 22 and/or the retractor extenders24/25 are provided with an elongate slot 43 for engagement with aninsertion tool (not shown). Each tab member 27 is also equipped with anenlarged tooth element 49 which engages within corresponding grooves 29provided along the inner surface of the retractor blades 12, 16, 18.

The handle assembly 20 may be coupled to any number of mechanisms forrigidly registering the handle assembly 20 in fixed relation to theoperative site, such as through the use of an articulating arm mountedto the operating table. The handle assembly 20 includes first and secondarm members 26, 28 hingedly coupled via coupling mechanism showngenerally at 30. The cephalad-most retractor blade 16 is rigidly coupled(generally perpendicularly) to the end of the first arm member 26.

The caudal-most retractor blade 18 is rigidly coupled (generallyperpendicularly) to the end of the second arm member 28. The posteriorretractor blade 12 is rigidly coupled (generally perpendicularly to) atranslating member 17, which is coupled to the handle assembly 20 via alinkage assembly shown generally at 14. The linkage assembly 14 includesa roller member 34 having a pair of manual knob members 36 which, whenrotated via manual actuation by a user, causes teeth 35 on the rollermember 34 to engage within ratchet-like grooves 37 in the translatingmember 17. Thus, manual operation of the knobs 36 causes the translatingmember 17 to move relative to the first and second arm members 26, 28.

Through the use of handle extenders 31, 33 (FIG. 8), the arms 26, 28 maybe simultaneously opened such that the cephalad-most and caudal-mostretractor blades 16, 18 move away from one another. In this fashion, thedimension and/or shape of the operative corridor 15 may be tailoreddepending upon the degree to which the translating member 17 ismanipulated relative to the arms 26, 28. That is, the operative corridor15 may be tailored to provide any number of suitable cross-sectionalshapes, including but not limited to a generally circular cross-section,a generally ellipsoidal cross-section, and/or an oval cross-section.Optional light emitting devices 39 may be coupled to one or more of theretractor blades 12, 16, 18 to direct light down the operative corridor15.

FIG. 9 illustrates an initial distraction assembly 40 forming part ofthe surgical access system according to the present invention. Theinitial distraction assembly 40 includes a K-wire 42, an initialdilating cannula 44 with handle 46, and a split-dilator 48 housed withinthe initial dilating cannula 44. In use, the K-wire 42 and split-dilator48 are disposed within the initial dilating cannula 44 and the entireassembly 40 advanced through the tissue towards the surgical target site(i.e. annulus). One exemplary method for advancing an initial dilatortowards a spinal target site is described in more detail later inconnection with FIGS. 23-50. Again, this is preferably accomplishedwhile employing the nerve detection and/or direction features describedabove. After the initial dilating assembly 40 is advanced such that thedistal ends of the split-dilator 48 and initial dilator 44 arepositioned within the disc space (FIG. 9), the initial dilator 44 andhandle 46 are removed (FIG. 10) to thereby leave the split-dilator 48and K-wire 42 in place. As shown in FIG. 11, the split-dilator 48 isthereafter split such that the respective halves 48 a, 48 b areseparated from one another to distract tissue in a generallycephalad-caudal fashion relative to the target site. The split dilator48 may thereafter be relaxed (allowing the dilator halves 48 a, 48 b tocome together) and rotated such that the dilator halves 48 a, 48 b aredisposed in the anterior-posterior plane. Once rotated in this manner,the dilator halves 48 a, 48 b are again separated to distract tissue ina generally anterior-posterior fashion. Each dilator halve 48 a, 48 bmay be, according to the present invention, provided with one or moreelectrodes (preferably at their distal regions) equipped for use with anerve surveillance system, such as, by way of example, the type shownand described in the NeuroVision PCT Applications.

Following this initial distraction, a secondary distraction may beoptionally undertaken, such as via a sequential dilation system 50 asshown in FIG. 12.

According to the present invention, the sequential dilation system 50may include the K-wire 42, the initial dilator 44, and one or moresupplemental dilators 52, 54 for the purpose of further dilating thetissue down to the surgical target site. Once again, each component ofthe secondary distraction assembly 50 (namely, the K-wire 42, theinitial dilator 44, and the supplemental dilators 52, 54 may be,according to the present invention, provided with one or more electrodes(preferably at their distal regions) equipped for use with a nervesurveillance system, such as, by way of example, the type shown anddescribed in the NeuroVision PCT Applications.

As shown in FIG. 13, the retraction assembly 10 of the present inventionis thereafter advanced along the exterior of the sequential dilationsystem 50. This is accomplished by maintaining the retractor blades 12,16, 18 in a first, closed position (with the retractor blades 12-16 ingenerally abutting relation to one another). Once advanced to thesurgical target site, the sequential dilation assembly 50 may be removedand the shim element 22 engaged with the posterior retractor blade 12such that the distal end thereof extends into the disc space as shown inFIG. 14. At this point, the handle assembly 20 may be operated to movethe retractor blades 16, 18 into a second, open or “retracted” positionas shown generally in FIGS. 15-16. As one can see, the posteriorretractor blade 12 is allowed to stay in the same general positionduring this process, such that the cephalad-most and caudal-mostretractor blades 14, 16 move away from the posterior retractor blade 12.At this point, the narrow and wide retractor extenders 24, 25 may beengaged with the caudal-most retractor blade 18 and cephalad-mostretractor blade 16, respectively, as shown in FIGS. 17-18.

As mentioned above, any number of distraction components and/orretraction components (including but not limited to those describedherein) may be equipped to detect the presence of (and optionally thedistance and/or direction to) neural structures during the steps tissuedistraction and/or retraction. This is accomplished by employing thefollowing steps: (1) one or more stimulation electrodes are provided onthe various distraction and/or retraction components; (2) a stimulationsource (e.g. voltage or current) is coupled to the stimulationelectrodes; (3) a stimulation signal is emitted from the stimulationelectrodes as the various components are advanced towards or maintainedat or near the surgical target site; and (4) the patient is monitored todetermine if the stimulation signal causes muscles associated withnerves or neural structures within the tissue to innervate. If thenerves innervate, this may indicate that neural structures may be inclose proximity to the distraction and/or retraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist). Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the following commonly owned andco-pending NeuroVision PCT Applications referenced above. In any case(visual monitoring, traditional EMG and/or surgeon-driven EMGmonitoring), the access system of the present invention mayadvantageously be used to traverse tissue that would ordinarily bedeemed unsafe or undesirable, thereby broadening the number of mannersin which a given surgical target site may be accessed. For example, thesurgical access system may be advantageously used to traverse tissuethrough the retroperitoneal space and the psoas muscle during asubstantially lateral, retroperitoneal approach to the lumbar spine, asshown in FIGS. 23-50.

FIGS. 19-20 illustrate, by way of example only, a monitoring system 120of the type disclosed in the NeuroVision PCT Applications suitable foruse with the surgical access system 10 of the present invention. Themonitoring system 120 includes a control unit 122, a patient module 124,and an EMG harness 126 and return electrode 128 coupled to the patientmodule 124, and a cable 132 for establishing electrical communicationbetween the patient module 124 and the surgical access system of thepresent invention (retractor assembly 10 of FIG. 1 and distractionassemblies 40, 50 of FIGS. 9-12). More specifically, this electricalcommunication can be achieved by providing, by way of example only, ahand-held stimulation controller 152 capable of selectively providing astimulation signal (due to the operation of manually operated buttons onthe hand-held stimulation controller 152) to one or more connectors 156a, 156 b, 156 c. The connectors 156 a, 156 b, 156 c are suitable toestablish electrical communication between the hand-held stimulationcontroller 152 and (by way of example only) the stimulation electrodeson the K-wire 42, the dilators 44, 48, 52, 54, the retractor blades 12,16, 18 and/or the shim members 22, 24, 25 (collectively “surgical accessinstruments”).

In order to use the monitoring system 120, then, these surgical accessinstruments must be connected to the connectors 156 a, 156 b and/or 156c, at which point the user may selectively initiate a stimulation signal(preferably, a current signal) from the control unit 122 to a particularsurgical access instruments.

Stimulating the electrode(s) on these surgical access instrumentsbefore, during and/or after establishing operative corridor will causenerves that come into close or relative proximity to the surgical accessinstruments to depolarize, producing a response in a myotome associatedwith the innervated nerve.

The control unit 122 includes a touch screen display 140 and a base 142,which collectively contain the essential processing capabilities(software and/or hardware) for controlling the monitoring system 120.The control unit 122 may include an audio unit 118 that emits soundsaccording to a location of a surgical element with respect to a nerve.The patient module 124 is connected to the control unit 122 via a datacable 144, which establishes the electrical connections andcommunications (digital and/or analog) between the control unit 122 andpatient module 124. The main functions of the control unit 122 includereceiving user commands via the touch screen display 140, activatingstimulation electrodes on the surgical access instruments, processingsignal data according to defined algorithms, displaying receivedparameters and processed data, and monitoring system status and reportfault conditions. The touch screen display 140 is preferably equippedwith a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 140 and/or base 142 may contain patient module interfacecircuitry (hardware and/or software) that commands the stimulationsources, receives digitized signals and other information from thepatient module 124, processes the EMG responses to extractcharacteristic information for each muscle group, and displays theprocessed data to the operator via the display 140.

In one embodiment, the monitoring system 120 is capable of determiningnerve direction relative to one or more of the K-wire 42, the dilators44, 48, 52, 54, the retractor blades 12, 16, 18 and/or the shim elements22, 24, 25 before, during and/or following the creation of an operativecorridor to a surgical target site. Monitoring system 120 accomplishesthis by having the control unit 122 and patient module 124 cooperate tosend electrical stimulation signals to one or more of the stimulationelectrodes provided on these instruments. Depending upon the location ofthe surgical access system 10 within a patient (and more particularly,to any neural structures), the stimulation signals may cause nervesadjacent to or in the general proximity of the surgical access system 10to depolarize. This causes muscle groups to innervate and generate EMGresponses, which can be sensed via the EMG harness 126. The nervedirection feature of the system 120 is based on assessing the evokedresponse of the various muscle myotomes monitored by the system 120 viathe EMG harness 126.

By monitoring the myotomes associated with the nerves (via the EMGharness 126 and recording electrode 127) and assessing the resulting EMGresponses (via the control unit 122), the surgical access system 10 iscapable of detecting the presence of (and optionally the distant and/ordirection to) such nerves. This provides the ability to activelynegotiate around or past such nerves to safely and reproducibly form theoperative corridor to a particular surgical target site, as well asmonitor to ensure that no neural structures migrate into contact withthe surgical access system 10 after the operative corridor has beenestablished. In spinal surgery, for example, this is particularlyadvantageous in that the surgical access system 10 may be particularlysuited for establishing an operative corridor to an intervertebraltarget site in a postero-lateral, trans-psoas fashion so as to avoid thebony posterior elements of the spinal column. For example, one suchoperative corridor to an intervertebral target site may be establishedthrough the retroperitoneal space and the psoas muscle during asubstantially lateral, retroperitoneal approach to the lumbar spine, asshown in FIGS. 23-50.

FIGS. 21-22 are exemplary screen displays (to be shown on the display140) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIGS. 19-20.These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 180 (in this case “DIRECTION”), a graphical representationof a patient 181, the myotome levels being monitored 182, the nerve orgroup associated with a displayed myotome 183, the name of theinstrument being used 184 (in this case, a dilator 46, 48), the size ofthe instrument being used 185, the stimulation threshold current 186, agraphical representation of the instrument being used 187 (in this case,a cross-sectional view of a dilator 44, 48) to provide a reference pointfrom which to illustrate relative direction of the instrument to thenerve, the stimulation current being applied to the stimulationelectrodes 188, instructions for the user 189 (in this case, “ADVANCE”and/or “HOLD”), and (in FIG. 22) an arrow 190 indicating the directionfrom the instrument to a nerve. This information may be communicated inany number of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 184), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 140 during the use of any or all of the various instrumentsforming the surgical access system 10 of the present invention,including the initial distraction assembly 40 (i.e. the K-wire 42 anddilators 44, 48) and/or the retractor blades 12, 16, 18 and/or the shimelements 22, 24, 25.

Referring now to FIGS. 23-50, some embodiments of the surgical accesssystem 10 may be particularly suited for establishing an operativecorridor to a surgical target site in the spine. Such an operativecorridor may be established through the retroperitoneal space and thepsoas muscle during a direct lateral, retroperitoneal approach to thespine. A surgeon may have direct visualization of the patient's anatomywithout the cumbersome requirements associated with using endoscopes oroperating coaxial through narrow tubes. Moreover, when using the accesssystem 10 through a lateral approach to the spine, the potential ofdamaging nerves while advancing instruments through the psoas muscle maybe substantially reduced. It will, of course, be appreciated that thesurgical access system and related methods of the present invention mayfind applicability in any of a variety of surgical and/or medicalapplications such that the following description relative to the directlateral, retroperitoneal approach to the spine is not to be limiting ofthe overall scope of the present invention.

When accessing a spinal target site via the substantially lateral,retroperitoneal approach described in connection with FIGS. 23-50, thesurgeon should consider several anatomical reference points, such as theiliac crest, the twelfth rib, and the lateral border of the erectorspinae muscle groups. In certain embodiments, blunt finger dissection isused to pass between these muscle groups and access the retroperitonealspace. Such a technique offers simple access to the retroperitonealspace while minimizing the potential of visceral lesion. Furthermore, insuch embodiments, the finger may be used to escort one or more dilatorsthrough the retroperitoneal space, thus reducing the potential ofperitoneal disruption. In some instances, each dilator is preferablyadvanced through the psoas muscle between the middle and anterior thirdof the muscle so that the nerves of the lumbar plexus are locatedposterior and outside the operative corridor. A monitoring system 120 ofthe type disclosed in the NeuroVision PCT Applications may be used toavoid damage to any peripheral nerves embedded throughout the psoasmuscle as the dilator is advanced through the muscle to the surgicaltarget site in the spine.

Referring now to FIGS. 23-24, a patient 200 is positioned on a surgicaltable 250 in preparation of spinal surgery. In some embodiments, acushion 252 is positioned between the patient's lateral side and thesurgical table 250 to arrange the patient 200 in such a way as toincrease the distance between the patient's iliac crest 202 and rib cage204. Alternatively, a flexion of the surgical table 250 may be used toaccomplish the desired arrangement. Such an arrangement helps to openthe invertebral disc space 206 at or near the surgical target site.

Referring to FIG. 25, an articulating arm assembly 60 is coupled to thesurgical table 250 to maintain the access system 10 in a substantiallyfixed position relative to the surgical target site when the operativecorridor has been established. In this embodiment, the articulating armassembly 60 is mounted to a bedrail 254 of the surgical table 250. Insome instances, a fluoroscopy system 260 is disposed proximal to thesurgical table 250 to provide the surgeon with visualization of thesurgical target area. This fluoroscopy system 260 includes a displaymonitor 262 that is positioned such that the surgeon may view themonitor 262 during the operation. In addition, a monitoring system 120of the type disclosed in the NeuroVision PCT Applications may bepositioned near the surgical table 250 so that the surgeon may view adisplay 140 of the monitoring system 120 during the operation.

Referring now to FIGS. 26-28, one or more instruments, such as K-wires42, are positioned laterally over an area of the patient 200 and thenviewed using the lateral fluoroscopy. The instruments are used toidentify a lateral incision location 208 that is substantially lateralto the surgical target site (e.g., the invertebral disc space 206). Asshown in FIG. 28, a first mark is made on the patient 200 at the lateralincision location 208. In addition, a second mark is made on the patientat a posteriolateral incision location 209 near the lateral incisionlocation 208. In this embodiment, the posteriolateral incision location209 is approximately at the lateral border of the erector spine muscle.Preferably, the posteriolateral incision location 209 is within afinger's length of the lateral incision location 208.

Referring to FIG. 29, an incision is made at the posteriolateralincision location 209, and the subcutaneous layers 210 are dissecteduntil reaching the muscular masses 212. A dissection instrument, such asblunt dissection scissors 270, is used to spread the muscle fibers 212until the retroperitoneal space 215 is reached. Preferably, the surgeonuses great caution to avoid perforation of the peritoneum 214.

Referring to FIGS. 30-31, after the retroperitoneal space 215 isreached, a guide member 275 is inserted through the posteriolateralincision 209 into the retroperitoneal space 215. In a presentlypreferred embodiment, the guide member is a finger 275 of the surgeon,which is preferably covered with a surgical glove for hygienic purposes.In other embodiments, the guide member 275 may be an instrument or toolconfigured to extend and maneuver in the retroperitoneal space asdescribed herein. As shown in FIGS. 30-31, the finger 275 may sweep aportion of the retroperitoneal space 215 and then palpate down to thepsoas muscle 220. This motion of the finger 275 in the retroperitonealspace 215 may loosen some fatty tissue before a dilator is advancedtherethrough.

Referring to FIGS. 32-33, after the psoas muscle 220 is identified, thefinger 275 is swept away from the psoas muscle 220 toward the lateralincision location 208. A scalpel 272 or other like instrument is used tomake and incision at this location 208. The incision should be of asufficient size to receive a distal end 41 an initial dilator 40.

Referring to FIGS. 34-35, the finger 275 is used to direct the distalend 41 of the initial dilator 40 through the retroperitoneal space 215toward the psoas muscle 220. In the presently preferred embodiment, theinitial dilator 40 includes at least a K-wire 42 and may also include asplit-dilator 48 slideably passed over the K-wire 42 (see, for example,FIG. 10). As shown in FIG. 34, the distal end 41 is introduced throughthe lateral incision location 208 and directed to the finger 275 in theretroperitoneal space 215. As shown in FIG. 35, the finger 275 engagesthe initial dilator 40 proximal to the distal end 41 and guides thedistal end 41 to the psoas muscle 220. By escorting the dilator 40through the retroperitoneal space 215 using the finger 275, thepotential for breaching or disrupting the peritoneal is reduced. Uponreaching the psoas muscle 220, the location of the distal end 41relative to the target site may be verified using an imaging system,such as an image intensifier.

Referring to FIGS. 36-37, the distal end 41 of the initial dilator 40 isadvanced in a substantially lateral direction through the psoas muscle220 toward the invertebral disc space 206 at or near the surgical targetsite. In the presently preferred embodiment, the fibers of the psoasmuscle 220 are split using blunt dissection and NeuroVisionneurophysiologic monitoring of the type disclosed in the NeuroVision PCTApplications. A stimulation connector 156 of the NeuroVision monitoringsystem 120 (see FIG. 19) is coupled to the initial dilator 40 to providea stimulation signal 157 as the dilator 40 is advanced through the psoasmuscle 220. It should be understood that the stimulation signal 157 isdepicted in FIG. 36 for illustrative purposes and is generally notvisible.

Descending nerves of the lumbar plexus normally lie in the posteriorone-third of the psoas muscle 220. The NeuroVision monitoring system 120of the type disclosed in the NeuroVision PCT Applications assists withthe safe passage by these nerves and/or confirmation of the nerves'posterior location. The NeuroVision monitoring system 120 willcontinuously search for the stimulus threshold that elicits an EMGresponse on the myotomes monitored and then reports such thresholds on adisplay 140 as shown in FIG. 37. As the dilator is advanced through thepsoas muscle 220, the stimulus necessary to elicit an EMG response willvary with distance from the nerve. In the presently preferredembodiment, experience has shown that threshold values greater than 10mA indicate a distance that allows for safe passage through the psoasmuscle 220 and continued nerve safety.

Referring to FIGS. 38-40, a K-wire 42 of the initial dilator 40 isintroduced into the targeted disc space 206 after the dilator 40 ispassed through the psoas muscle 220. Preferably, the position of thedistal end 41 of the dilator 40 is confirmed using fluoroscopic imagingbefore the K-wire 42 is introduced into the disc space 206. After adistal portion of the K-wire 42 is inserted into the targeted disc space206, depth markings 45 (FIG. 39) on the dilator 40 may be read at theskin level to determine the appropriate length of retractor blades 12,16, 18 that will be used with the handle assembly 20 of the accesssystem 10. As shown in FIG. 40, the appropriate length blades 12, 16,and 18 may be secured to the handle portion 20 by tightening fastenerswith a driver instrument 274.

Referring to FIG. 41, the sequential dilation system 50 (previouslydescribed in connection with FIG. 12), including one or moresupplemental dilators 52, 54, may be guided over the initial dilator 40for the purpose of further dilating the tissue down to the surgicaltarget site. In the presently preferred embodiment, the NeuroVisionmonitoring system 120 of the type disclosed in the NeuroVision PCTApplications is used with the supplemental dilators 52, 54 to providesafe passage through the psoas muscle 220. The initial dilator 40 andthe supplemental dilators 52, 54 are advanced through the lateralincision location 208 to the targeted disc space 206 in a substantiallylateral direction to create a distraction corridor.

Still referring to FIG. 41, the retractor blades 12, 16, 18 of theaccess system 10 are introduced over the supplemental dilator 54 (or theinitial dilator 40 if the sequential dilation system 50 is not employed)toward the disc space 206. Again, the NeuroVision monitoring system 120of the type disclosed in the NeuroVision PCT Applications may be usedwith the blades 12, 16, 18 to provide safe passage through the psoasmuscle 220. In some embodiments, the posterior shim element 22 and/orthe retractor extenders 24, 25 are engaged with the retractor blades 12,16, 18 (as previously described in connection with FIGS. 1-7). After theretractor blades 12, 16, 18 are introduced along the distractioncorridor, fluoroscopic imaging may be used to confirm the position ofthe blades 12, 16, 18 proximal to the disc space 206.

Referring to FIG. 42, the articulating arm assembly 60 is coupled to thehandle member 20 of the access system 10. As previous described inconnection with FIG. 25, the articulating arm assembly 60 is alsocoupled to the surgical table 250 so as to maintain the access system 10in a substantially fixed position. Handles 62 and 64 may be turned tosubstantially fix the position of articulating arm assembly 60.

Referring now to FIGS. 43-44, handle extenders 31 and 33 may be squeezeto spread the blades 12, 16, 18 and knob members 36 may be turned toselectively adjust the posterior retractor blade 12 (previouslydescribed in connection with FIGS. 13-18). Such movement by the blades12, 16, 18 retracts the distraction corridor so as to form an operativecorridor 15.

FIG. 45 shows a lateral view of the operative corridor 15 down to thetargeted disc space 206 in the patient's spine. Light emitting devices39 may be coupled to one or more of the retractor blades 12, 16, 18 todirect light down the operative corridor 15. In this embodiment, thelight emitting devices 39 are coupled to a xenon arthroscopy lightsource. The surgeon may use direct visualization and/or a NeuroVisionprobe of the type disclosed in the NeuroVision PCT Applications toconfirm that the operative corridor 15 is neurologically clear.

Referring to FIGS. 46-50, various instruments may be inserted throughthe operative corridor 15 to prepare the targeted disc space 206. In thepresently preferred embodiment, the operative corridor 15 has a 15-20mmannulotomy to provide ample space for the various instruments. In otherembodiments, the operative corridor 15 may have other configurations,depending on the surgical task to be performed.

In this embodiment depicted in FIGS. 46-50, the disc space 206 isundergoing a discectomy and insertion of a spinal implant. As shown inFIG. 46, at least one preparation tool 276 such as a disc cutter,pituitary, scraper, curette, or the like is inserted through theoperative corridor 15 to prepare the disc space 206. Referring moreclosely to FIG. 47, one or more sizers 277 are inserted to the discspace 206 to provide appropriate disc height restoration. As shown inFIG. 48, a broach 278 may be used in the disc space 206 to removeosteophytes and to facilitate implant insertion.

Referring now to FIGS. 49-50, an appropriately sized implant 282 isadvanced into the disc space 206 with an inserter tool 280. The implant282 is releasably secured to the inserter tool 280 such that the surgeonmay release the implant when it is properly positioned in the disc space206. The implant may comprise a material that facilitates bone fusion(such as allograft or autograft), and autograft or graft extenders maybe used in the disc space 206 after the implant is inserted.

After the procedure on the targeted disc space 206 is complete, theaccess system 10 is carefully removed from the operative corridor 15.Direct visualization may be used to confirm the absence of significantbleeding in the disc space 206 or the psoas muscle 220. The skin aroundthe operative corridor may be closed using a suturing method, such as asubcuticular suture.

Accordingly, certain methods of using the access system 10 can safelyand effectively establish a minimally invasive operative corridorthrough the retroperitoneal space 215 and the psoas muscle 220 via adirect lateral, retroperitoneal approach to the spine. Such a methodallows the surgeon to directly visualize the patient's anatomy withoutthe cumbersome requirements associated with using endoscopes oroperating coaxial through narrow, artificial tube. Moreover, whenemploying such a method to laterally approach the spine, the potentialof damaging nerves while advancing dilators and other instrumentsthrough the psoas muscle 220 may be substantially reduced.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of gaining access a surgical target site in afashion less invasive than traditional “open” surgeries and, moreover,does so in a manner that provides the ability to access such a surgicaltarget site regardless of the neural structures required to be passedthrough (or near) in order to establish an operative corridor to thesurgical target site. The present invention furthermore provides theability to perform neural monitoring in the tissue or regions adjacentthe surgical target site during any procedures performed after theoperative corridor has been established. The surgical access system ofthe present invention can be used in any of a wide variety of surgicalor medical applications, above and beyond the spinal applicationsdiscussed herein. Such spinal applications may include any procedurewherein instruments, devices, implants and/or compounds are to beintroduced into or adjacent the surgical target site, including but notlimited to discectomy, fusion (including PLIF, ALIF, TLIF and any fusioneffectuated via a lateral or far-lateral approach and involving, by wayof example, the introduction of bone products (such as allograft orautograft) and/or devices having ceramic, metal and/or plasticconstruction (such as mesh) and/or compounds such as bone morphogenicprotein), total disc replacement, etc.).

Moreover, the surgical access system of the present invention opens thepossibility of accessing an increased number of surgical target sites ina “less invasive” fashion by eliminating or greatly reducing the threatof contacting nerves or neural structures while establishing anoperative corridor through or near tissues containing such nerves orneural structures. In so doing, the surgical access system of thepresent invention represents a significant advancement capable ofimproving patient care (via reduced pain due to “less-invasive” accessand reduced or eliminated risk of neural contact before, during, andafter the establishment of the operative corridor) and lowering healthcare costs (via reduced hospitalization based on “less-invasive” accessand increased number of suitable surgical target sites based on neuralmonitoring). Collectively, these translate into major improvements tothe overall standard of care available to the patient population, bothdomestically and overseas.

What is claimed is:
 1. A method of forming and using an operativecorridor through a retroperitoneal space and a psoas muscle during asubstantially lateral, retroperitoneal approach to a lumbar spine, themethod comprising: while a user's finger is inserted through a skinincision, moving a tip portion of the user's finger through bodilytissue that is generally lateral from a lumbar spine for blunt fingerdissection of the bodily tissue proximate to a retroperitoneal space;advancing the tip portion of the user's finger into the retroperitonealspace so as to palpate to a psoas muscle; advancing an elongatestimulation instrument along a lateral, trans-psoas path through theretroperitoneal space, through the psoas muscle, and to the lumbar spinesuch that a distal tip portion of the elongate stimulation instrumentengages an annulus of a spinal disc of the lumbar spine, the distal tipportion of the elongate stimulation instrument including a stimulationelectrode that outputs electrical stimulation for nerve monitoringduring advancement of the elongate stimulation instrument through thepsoas muscle; advancing a dilator system along the lateral, trans-psoaspath to the lumbar spine to create a distraction corridor, the dilatorsystem comprising at least one dilator that slidably engages an exteriorof the elongate stimulation instrument, the at least one dilator beingadvanced to the spinal disc along the lateral, trans-psoas path to thelumbar spine; slidably advancing a three-bladed retractor assembly overthe dilator system toward the spinal disc along the lateral, trans-psoaspath, the three-bladed retractor assembly including a posterior-mostretractor blade, a caudal-most retractor blade, and a cephalad-mostretractor blade that extend generally perpendicularly relative to armmembers of a blade holder apparatus, wherein the three-bladed retractorassembly is slidably advanced over the dilator system when in a firstposition in which the posterior-most retractor blade, the caudal-mostretractor blade, and the cephalad-most retractor blade are positioned tosimultaneously advance over the dilator system; and adjusting the bladeholder apparatus to shift the three-bladed retractor assembly to asecond position in which the caudal-most retractor blade and thecephalad-most retractor blade are spaced apart from the posterior-mostretractor blade to enlarge the distraction corridor and form anoperative corridor along the lateral, trans-psoas path to the lumbarspine.
 2. The method of claim 1, wherein the step of adjusting the bladeholder apparatus comprises squeezing handle portions of the blade holderapparatus toward one another so that the caudal-most retractor blade andthe cephalad-most retractor blade move away from the posterior-mostretractor blade.
 3. The method of claim 2, further comprising releasablyengaging a posterior shim element with the posterior-most retractorblade so that at least a portion of the posterior shim element extendsdistally from the posterior-most retractor blade and anchors into thespinal disc.
 4. The method of claim 3, wherein the step of releasablyengaging the posterior shim element is performed prior to the step ofadjusting the blade holder apparatus to shift the three-bladed retractorassembly to the second position.
 5. The method of claim 3, furthercomprising releasably engaging a first retractor blade extender with thecaudal-most retractor blade so that at least a portion of the firstretractor blade extender protrudes from the caudal-most retractor blade,and releasably engaging a second retractor blade extender with thecephalad-most retractor blade so that at least a portion of the secondretractor blade extender protrudes from the cephalad-most retractorblade.
 6. The method of claim 5, wherein the first and second retractorblade extenders inhibit ingress of tissue into the operative corridorafter the three-bladed retractor assembly is adjusted to the secondposition.
 7. The method of claim 1, wherein the step of moving the tipportion of the user's finger through the bodily tissue separates fattytissue before the elongate stimulation instrument is advanced into theretroperitoneal space.
 8. The method of claim 1, wherein the step ofadjusting the blade holder apparatus comprises: pivoting two of the armmembers of the blade holder apparatus so as to move the caudal-mostretractor blade and the cephalad-most retractor blade away from theposterior-most retractor blade, and rotating a knob element on the bladeholder apparatus so as to linearly move the posterior-most retractorblade relative to the caudal-most retractor blade and the cephalad-mostretractor blade.
 9. The method of claim 1, wherein the step of advancingthe elongate stimulation instrument comprises delivering the elongatestimulation instrument together with the at least one dilator cannulaalong the lateral, trans-psoas path to the lumbar spine.
 10. The methodof claim 1, further comprising: activating a nerve monitoring systemthat delivers an electrical stimulation signal to the stimulationelectrode of the elongate member during delivery of the elongate memberalong the lateral, trans-psoas path to the lumbar spine, the nervemonitoring system detecting electromyographic activity via a set ofsensor electrodes in leg muscle myotomes associated with nerves in thevicinity of the spinal disc; and viewing a video display device of thenerve monitoring system that contemporaneously displays: a numericstimulation threshold required to obtain the electromyographic activityin at least one of said leg muscle myotomes, and myotomes levels beingmonitored.
 11. A method of forming and using an operative corridorthrough a retroperitoneal space and a psoas muscle during asubstantially lateral, retroperitoneal approach to a lumbar spine, themethod comprising: while a user's finger is inserted through a skinincision, moving a tip portion of the user's finger through bodilytissue in a retroperitoneal space that is generally lateral from alumbar spine and advancing the tip portion of the user's finger topalpate to a psoas muscle that is generally lateral from a lumbar spine;advancing a dilator system along the lateral, trans-psoas path to thelumbar spine to create a distraction corridor, the dilator systemcomprising: an initial dilator that is advanced through the psoas muscleto a spinal disc of the lumbar spine, a first supplemental dilator thatslidably advances along the lateral, trans-psoas path over an exteriorof the initial dilator, and a second supplemental dilator that slidablyadvances along the lateral, trans-psoas path over an exterior of thefirst supplemental dilator, wherein at least the initial dilatorincludes a stimulation electrode that outputs electrical stimulation fornerve monitoring when the initial dilator is positioned in the psoasmuscle; slidably advancing a three-bladed retractor assembly over anexterior of an outermost dilator of the dilator system toward the spinaldisc along the lateral, trans-psoas path, the three-bladed retractorassembly including a posterior-most retractor blade, a caudal-mostretractor blade, and a cephalad-most retractor blade that extend from ablade-holder apparatus, wherein the three-bladed retractor assembly isslidably advanced over the dilator system when in a first position inwhich the posterior-most retractor blade, the caudal-most retractorblade, and the cephalad-most retractor blade are positioned tosimultaneously advance over the outermost dilator of the dilator system;and adjusting the blade-holder apparatus of the three-bladed retractorassembly so as to shift the three-bladed retractor assembly to a secondposition in which the caudal-most retractor blade and the cephalad-mostretractor blade are spaced away from the posterior-most retractor bladeto enlarge the distraction corridor and form an operative corridor alongthe lateral, trans-psoas path to the lumbar spine.
 12. The method ofclaim 11, wherein an inner wire member is received within a centrallumen of the initial dilator and penetrates laterally into an annulus ofthe spinal disc of the lumbar spine prior to advancing the first andsecond supplemental dilators.
 13. The method of claim 11, furthercomprising adjusting a position of a first retractor blade extenderremovably attached to the caudal-most retractor blade so that at least aportion of the first retractor blade extender protrudes from thecaudal-most retractor blade, and adjusting a position of a secondretractor blade extender removably attached to the cephalad-mostretractor blade so that at least a portion of the second retractor bladeextender protrudes from the cephalad-most retractor blade.
 14. Themethod of claim 13, wherein the first and second retractor bladeextenders inhibit ingress of tissue into the operative corridor afterthe three-bladed retractor assembly is adjusted to the opened position.15. The method of claim 11, wherein the step of moving the tip portionof the user's finger through the bodily tissue separates fatty tissue inthe retroperitoneal space before the initial dilator is advanced intothe retroperitoneal space.
 16. The method of claim 11, furthercomprising activating a light emitting device to direct light throughthe operative corridor toward the spinal disc, the light emitting devicebeing coupled to one of the cephalad-most retractor blade and thecaudal-most retractor blade.
 17. The method of claim 11, wherein thestep of adjusting the blade-holder apparatus comprises rotating a knobelement of the blade-holder apparatus relative to a linear rack memberof the blade-holder apparatus.
 18. The method of claim 11, furthercomprising: activating a nerve monitoring system that delivers anelectrical stimulation signal to the stimulation electrode of theinitial dilator during advancement of the initial dilator through thepsoas muscle, the nerve monitoring system detecting electromyographicactivity via a set of sensor electrodes in leg muscle myotomesassociated with nerves in the vicinity of the spinal disc; and viewing avideo display device of the nerve monitoring system that displaysinformation in response to the electromyographic activity in at leastone of said leg muscle myotomes.
 19. The method of claim 11, wherein theskin incision through which the user's finger is inserted is differentfrom a skin penetration point of the initial dilator.
 20. The method ofclaim 11, wherein the first and second supplemental dilators includestimulation electrodes that output electrical stimulation for nervemonitoring.